Competitive interactions between cells in the avian ciliary ganglion are being studied by altering the balance between cells and their peripheral target. The effect of innervation on muscle individualization will be tested in chick embryos by performing spinal cord deletions. Lumbosacral motoneuron pools in the mouse will be determined with retrograde transport of HRP and the development of these motor projection patterns studied in embryos. The development of cutaneous and proprioceptive sensory innervation of the chick hindlimb will also be studied by a combination of electrophysiology and retrograde labelling of cell bodies with HRP. BIBLIOGRAPHIC REFERENCES: Landmesser, Lynn (1976) The development of neural circuits in the limb moving segments of the spinal cord. Adv. in Behav. Biol. 18:707-733. Landmesser, L. (1977) The development of motor projection patterns in the chick hindlimb. Neuroscience Abst. Vol III, in press.